Katherine Heigl had a rocky relationship with the writers of "Grey's Anatomy." Getty/Astrid Stawiarz

The INSIDER Summary:

Many TV shows have drama both on and off camera.

Sometimes it's the co-stars who don't see eye-to-eye with each other.

Other times, the stars have conflict with the creators or networks behind the show.

Audiences love the drama that they get from a weekly television series. If they're honest, the same audience also secretly loves the drama that happens behind the scenes as well.

Though every show wants to keep its stars and creators looking professional in the eyes of their viewers, there is no PR team capable of covering up every single embarrassing public breakdown, contentious pay dispute, and behind-the-scenes fight.

The feuds on this list aren't public feuds between unconnected celebrities, such as Rosie O'Donnell and Donald Trump, and they're not big-budget film clashes like the one between Charlize Theron and Tom Hardy in " Mad Max: Fury Road."

These are the feuds that boil up between TV creators and performers who have to work together for years on end, butting heads and arguing until their contracts are up or the show is cancelled. These feuds are the ones they tried (and failed) to keep hidden from their audiences.

Here are the 15 Most Shocking Behind-The-Scenes TV Feuds.

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15. John Belushi and the (female) "SNL" writers

The impact that John Belushi had on the television world for his work on " Saturday Night Live" is immense, as is the absence left in the wake of his tragic early death.

However, being a fantastic artist and comedian doesn't mean he wasn't also bigoted and problematic. Belushi was known for intentionally tanking sketches by female writers because he believed women writers simply couldn't be funny.

Though there were public rumors for years about Belushi's behavior on the show, the cast and creators generally kept quiet about it after his death, largely out of respect. In recent years, however, braver cast members have opened up about it, including Jane Curtin, during an appearance on Oprah.

She put it plainly: "he felt as though it was his duty to sabotage pieces that were written by women." The female cast and writers found longevity and fame in the industry, clearly proving Belushi wrong.

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14. William Shatner and the cast of "Star Trek"

Everyone remembers William Shatner as the brave adventurer Captain Kirk, boldly going where no man has gone before in the original " Star Trek" series. However, the reason for his memorable performance is much more complicated than fans might realize.

Shatner was notorious for taking away any lines and camera time he could from his cast members, assuring that Kirk was the focus of as much of the show as possible. This didn't sit well with the other cast members.

No one has had a longer-running feud with Shatner than co-star George Takei. In his autobiography, "To The Stars," Takei mentioned how Shatner would act like he didn't know who Takei was during the series.

The feud continued through the years, when Takei outed Shatner for snubbing an event to benefit an ailing James Doohan, and Shatner himself went on a YouTube tirade when he was supposedly not invited to Takei's wedding. These feuds started behind the scenes, but, with a personality like Shatner's, they were bound to eventually get some attention.

There's more than enough high-intensity drama to go around on " Grey's Anatomy," both in front of and behind the camera, but it was a behind-the-scenes fight between Isaiah Washington, Patrick Dempsey, and T.R. Knight that caught headlines and cost Washington his job.

What began as an argument about starting the shoot on time between Washington and Dempsey somehow turned towards Knight, at whom a gay slur was hurled.

He publicly apologized after the news broke of the dispute, and, if that had been the end of it, he may not have lost his job. However, in a Golden Globes cast interview following a win for the show, Washington felt the need to defend himself, denying that he called Knight the slur while at the same time repeating the slur publicly… again.

Though he obviously lost his job on the show, some fences were eventually mended and Washington returned for an episode seven years after he was fired.

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12. Gabe Kaplan is not welcome in "Welcome Back, Kotter"

Gabe Kaplan was a comedian who played the lovable, wisecracking teacher in "Welcome Back, Kotter" for four seasons. Though the cast started off strong and united, it didn't take long for cracks to form.

Marcia Strassman, who played Kotter's wife Julie, was miserable doing scenes with Kaplan. According to People, Strassman said that "it has always been hard to act with him, especially in intimate scenes. I hate the series. I pray every day for a cancellation."

After Strassman finally revealed the feud publicly during a press event, other cast members were forced to take sides as well.

It escalated to the point that the fourth and final season saw several Kaplan loyalists on the staff fired, and Kaplan himself was reduced to appearing in only a handful of episodes (despite having the show named after his character). Strassman somehow also ended up getting saddled with even more to do on a show she wanted out of. In this feud, there was no clear winner- everyone lost something.

11. Alec Baldwin and Tina Fey on "30 Rock"

Tina Fey took her experience as the head writer on "Saturday Night Live" to create the popular and hilarious " 30 Rock," choosing dramatic actor Alec Baldwin for a major comedic role in the show.

This might lead a viewer to believe that he would be appreciative of the career resurgence and opportunity. Baldwin, however, has often been known for his feuds, from President Donald Trump to Harrison Ford to his own daughter (who he screamed at in a voicemail that leaked and went viral).

Baldwin, unhappy with what he saw as a dip in creative quality, threatened to leave the series around season five. In a " Rolling Stone" interview, Baldwin said "I'm going to get the f**k out of here, I'm done. Because I'm an employee, I don't have any say."

Though he did return to the show, and there seems to be no bad blood between them now (Fey recommended Baldwin for the "SNL" gig as Trump), it was an unfortunate feud that Baldwin himself decided to make public.

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10. Nicollette Sheridan and Marc Cherry on "Desperate Housewives"

"Desperate Housewives" was a series which had premise filled with shocking twists and even more shocking secrets, and it was only a matter of time before these secrets spilled into the personal lives of the people who created it.

The show had its share of feuds (rumor has it that none of the housewives got along with Teri Hatcher), but one feud got so out of hand that it led to a legal battle when Nicollette Sheridan sued show creator Marc Cherry.

Sheridan filed a $20 million lawsuit, which stated that Cherry assaulted her on the set and noted that she was fired from the show after she attempted to report his behavior to the network. Sheridan allegedly reported the behavior to Disney, and, after a few weeks of investigation, her character was hastily written out of the series. The trial ended in a hung jury, and an attempted re-trial was tossed out of court.

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9. Shannen Doherty leaves "Charmed"

Three seasons into the popular fantasy series "Charmed," Shannen Doherty suddenly announced that she was leaving the series. With relatively little explanation from Doherty or the show about the departure, assumptions were made, many of which revolved around Doherty's abandonment of her previous Spelling Television series, "Beverly Hills 90210." While the exit may have looked like typical star behavior, the truth might have had more to do with her co-workers.

There were longtime rumors that Doherty didn't get along with co-star Alyssa Milano, but a recent interview on Bravo's "Watch What Happens Live" gave Milano a chance to address it.

She called her experience on the show rough and akin to high school. Holly Combs, the third lead on the series, tweeted later about how she took the show very seriously.

After Doherty recently beat cancer, however, Milano said she contacted her and the feud has seemingly been put to rest.

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8. Naya Rivera and the cast of "Glee"

Fox

"Glee" was a show made up of stage performers and teenagers, each of whom were jockeying for attention and solos, and guided by showrunner Ryan Murphy. It was only a matter of time before troubles popped up.

Aside from the tragic death of Cory Monteith, the show saw shake-ups when Dianna Agron asked to leave the show and Mark Salling was arrested for possession of child pornography.

However, Naya Rivera was the cast member who was wrapped up in the most issues with the other actors. Aside from a reduced presence in season six of the show (which she reportedly requested herself), Rivera was constantly rumored to have trouble with Lea Michele.

Rivera discussed this in her book "Sorry Not Sorry: Dreams, Mistakes, and Growing Up," along with the time she covered Salling's car with pet food after they broke up.

Showrunner Murphy copped to the fact that the show always had issues with its cast.

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7. Thomas Gibson in "Criminal Minds"

People tune in to procedural dramas in the hopes of seeing butt-kicking detectives solving crimes. However, they rarely expect that the man playing the detective was committing crimes by actually kicking the writers of that show. This is exactly what happened on the set of "Criminal Minds," when star Thomas Gibson attacked writer Virgil Williams.

The situation began on set, where Gibson approached Williams about changing a line that he didn't like. According to Williams, he offered an alternative to Gibson which was rejected. Gibson had an idea of what he wanted, which Williams felt wouldn't work, and the situation became heated.

The next time Gibson passed Williams, he reportedly kicked him. He was suspended temporarily, with the network eventually opting not to bring him back to the show. Gibson disputes the intent, as well as both his and Williams' actions, and Williams has since admitted that he was once suspended from set for raising his voice.

This is certainly a circumstance where the full truth may never be clear.

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6. Victoria Jackson and fellow castmates on "SNL"

"Saturday Night Live" has had more than its share of feuds, issues, and drama, but the circumstances surrounding Victoria Jackson are unique, to say the least.

The sticking point between her and her fellow castmates was religious and political, something that can't help but come up on a show as satirical and politically-minded as "SNL." Though it began as mutual respect for each other's beliefs, it devolved into attempted religious conversion in the form of backstage arguments and passive-aggressive gifts like audiobook versions of the Bible.

Though the incidents might seem isolated and innocent enough, Jackson has only gotten more extreme in her public representation of her beliefs, which frequently stand in opposition to her former castmembers'.

In the years following the show, she was embraced by the Tea Party. However, her performance persona- as the silly-song singing ukelele player- confuses people on both sides of the political spectrum. The feud hasn't ended either; Jackson ended up being one of the only "SNL" cast members not in the main audience during the 40th anniversary TV special.

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5. Katherine Heigl and Shonda Rhimes on "Grey's Anatomy"

Though the Washington/Dempsey/Knight feud was a more shocking and highly covered issue, "Grey's Anatomy" has never been at a loss for controversy.

In the run-up to the Emmy nomination season, actress Katherine Heigl said she wouldn't be submitting herself for any awards because she didn't think the material she was given was worth rewarding. This obviously didn't go over well with creator and showrunner Shonda Rhimes.

When Heigl finally left the series in 2010, Rhimes apparently learned her lesson about only working with agreeable actors moving forward. Though there were two notable major shake-ups on "Grey's Anatomy," the same cannot be said of her others shows, such as "Scandal."

Shonda's interview with " Hollywood Reporter" sums up her perspective of the new working situation nicely: "there are no Heigls in this situation." These words are worth heeding for others, as Heigl famously bad-mouthed her feature film "Knocked Up" as well.

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4. Stana Katic and Nathan Fillion on "Castle"

While television viewers can get intensely invested in the personal relationships of the characters on their favorite shows, they're usually fully aware of the fact that on-screen romances don't necessarily translate to real life. However, the viewers expect that there is a camaraderie and professionalism in their favorite shows, and that has never been more untrue than with Nathan Fillion and Stana Katic during the run of "Castle."

When "Castle" was canceled after eight seasons, it happened because Katic wasn't going to return to the series, and rumors began to circulate about the terrible relationship between the leads.

Reports surfaced that Katic and Fillion refused to speak to each other off the set, Katic was purportedly driven to tears, and the two cast members were even sent to couples counselling so that they could get along through the television show. They both kept a professional demeanor in the wake of the cancellation, but it's hard to separate the on-screen couple from the off-screen animosity.

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3. Penny Marshall and Cindy Williams in "Laverne & Shirley"

Shows about best friends are always held to higher scrutiny for the actors portraying them, and, in the case of "Laverne & Shirley," the gap between the titular characters and their actresses Penny Marshall and Cindy Williams was vast.

Because the creator of the show, Garry Marshall, is Penny's brother, it made sense that Penny would end up a lead on his show. Williams, however, always claimed that Penny wanted her gone so that the attention and spotlight would be on Penny alone.

Whether this was always true or not, this is exactly how the show ended. Williams became pregnant at the beginning of the eighth season, and fought with the studio in order to get some time off, but was ultimately refused.

She left the show, filed a $20 million lawsuit against the studio, and eventually settled out of court and got out of her contract. So the show called "Laverne & Shirley" ended with Laverne alone and Shirley nowhere to be found.

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2. Dan Harmon, Chevy Chase, and the network of "Community"

It was a long shot that " Community" was going to find an audience and stick around for longer than a season. It became even more unlikely once the show found its tone a few episodes in, a niche meta-comedy that was determined to buck every trend and avoid every expectation.

This didn't make show creator Dan Harmon very popular with the network, who wanted a simple concept to market. The network wasn't the only issue Harmon would run into, though.

He and cast member Chevy Chase had a contentious relationship, one which Harmon revealed publicly by playing an expletive-filled voicemail from Chase to a podcast audience.

It was no coincidence that, in the wake of that incident, Chase and the network agreed that Chase wouldn't be returning to the show. It turns out, the same was true of Harmon, who was fired from the show because of tensions between him and the studio.

Harmon eventually returned to the show after a year off, and Chase had a cameo appearance in a later episode, but the controversy still brews.

How could it be true- two of the defenders of Sunnydale, a skilled witch and a Slayer, aren't really best friends? Well, they started out well enough. Sarah Michelle Gellar and Alyson Hannigan got along well during the early days of " Buffy the Vampire Slayer."

Then both their stars began receiving work outside of the show, with Gellar appearing in "Cruel Intentions" and "Scooby-Doo" and Hannigan starring in the enormously successful "American Pie" series. The two had steady external careers and plenty of sway, but they eventually began butted heads during the shooting of the show, with Hannigan saying that Gellar had been unhappy since season three.

However, the big offense came when Gellar announced in "Entertainment Weekly" that season seven would be the last one… without notifying the cast and crew. Hannigan commented on it publicly, but show creator Joss Whedon came to Gellar's defense, saying it was his responsibility to tell her and that he had dropped the ball. To Gellar's credit, she says she has no ill will.